This invention relates to a self-tightening threaded fastener with multiple locking washers. In particular, it relates to a threaded nut having self-tightening means and a self-centering structure.
A variety of self-tightening fastening devices have been disclosed in the prior art. Such fastener devices accommodate a workpiece exposed to vibration. Some prior art devices may be found in U.S. Pat. No. 3,263,727 which issued to Arthur B. Herpolsheimer on Aug. 2, 1966; and U.S. Pat. No 3,417,802 which issued to Carl O. Oldenkott on Dec. 24, 1968. A commercially-available form of such device has long been marketed as a Disc-Lock, vibration proof, self-tightening, locking device.
Such devices usually have one or more washer-shaped pieces having inclined cams on one side and a series of ridges on the other. The washers are mounted so that the cam surfaces will mate. In a typical situation, the washers are mounted on a stud between a nut and the workpiece.
Vibration or shock will cause the stud or bolt to elongate. The nut tends to rotate loose. A self-tightening locking device prevents this since the cam rise angle is greater than the lead angle of the thread on the bolt. As the nut rotates relative to the washer, the preload is actually increased, further locking the nut.
When the bolt contracts, the inclined planes of the cam causes the nut to rotate back to its original position. The result is a fastening system that is vibration proof.
One shortcoming of a commercially available, self-tightening fastener is that it cannot be substituted for certain types of wheel nuts of the type having a raised partially spherical crown. The partially spherical crown is seated in a conical or spherical recess.
A form of a self-centering fastener assembly is disclosed in U.S. Pat. No. 4,362,449 which issued Dec. 7, 1982 to Emil J. Hlinsky.